A Most Unusual Lizard – the Crocodile, Armored or Casque-headed Skink

With over 1,200 species, the skink family (Scincidae) is the lizard world’s largest, and in it we find some very unusual creatures. Yet one, the Crocodile Skink (Tribolonotus gracilis), stands out as being particularly unique even in this odd assemblage of reptiles. Originally thought to be a difficult animal to keep, we are now learning more and more about it, and captive reproduction is no longer a rarity. Let’s take a look at how this skink distinguishes itself.

Description

This species departs radically from the typical skink body plan. The head is enlarged, triangular in shape and capped with helmet-like scales, while four rows of thick, pointed scales line the back. Its color is dark brown to black, with a striking red or orange area about the eye. Crocodile Skinks average 6.5-7.8 inches in length.

Range

The Crocodile Skink is found only in Papua New Guinea and on the nearby Admiralty Islands. One additional species, the Spiny Skink, T. novaeguinea, (which also appears in the pet trade) inhabits New Guinea, and 6 other species within the genus are found on the Solomon Islands and in New Caledonia.

Habitat

Again unlike most skinks, they are largely nocturnal or crepuscular (active in early mornings and evenings). Although declining in some areas, recent observations indicate that piles of coconut husks on farms provide important habitat, and may help populations to increase.

Reproduction

Here again the rules are broken, with females laying only 1 egg at a time. Oddly, the left ovary and oviduct are somewhat regressed in development as compared to the right. The single egg developing on the left side is not laid until approximately 60 days after the right ovary’s egg has been laid. This is true for 7 of the 8 species of Tribolonotus…Schmidt’s Helmet Skink (T. schmidti) gives birth to a single live offspring. Well-fed female Crocodile Skinks may produce up to 6 eggs each year.

Female Crocodile Skinks guard their eggs during the 70 day incubation period. In captivity they cover the eggs with substrate when foraging and lunge at intruders. The hatchlings stay in close proximity to the female for approximately 2 weeks. Further study may reveal an even greater degree of social behavior, as males kept in the same enclosure are not hostile to the young or to the female.

Other Unusual Characteristics

Crocodile Skinks are unique among lizards in having glands under the abdominal scales, on the surface of the hands, and on the undersides of the feet. The function of these glands is not completely understood.

They also vocalize when disturbed – producing quite a loud “squawk” for such a small creature – and feign death when stressed. I can attest that both behaviors are very surprising to the uninitiated! Some vocalizations may be in response to egg disturbance – another lizard “first” (please see article below).

Further Reading

An interesting article detailing work carried out at the Dallas Zoo on Crocodile Skink vocalizations is posted here.

I’ve always provided them with UVB, but have never seen them bask…not sure if the need has been established or not but, unlike as with some amphibs, UVB does them no harm. They are extremely shy…some individuals will show themselves if provided thick cover, especially low-growing Pothos plants, under which they can move.

I had a number of wild caught specimens at the Bronx Zoo; they do seem very stress-prone, and some had a bad reaction to meds. Captive born or long-term captives definitely the way to go with these guys. Action figures – perfect!

I have a male and female crocodile skinks that are breeding age and I noticed that the male has started to chase the female and will hold her tail in his mouth, regardless of whether she tries to get away and while he’s doing this she will bob her head at him. I’m wondering if anyone else has seen this behaviour? My skinks also seem to be unusual in that my female rarely hides and neither seem to be nocturnal.

Thanks for your interest in our blog and for passing along your interesting observations.

What you describe is courtship behavior…males may also inflate their throats a bit and sometimes grab females about the neck. Males mature earlier than females (usually by age 3, females at age 4), so she may not be ready – However, even in well-matched pairs it often takes quite a bit of “wooing” on the part of the male before mating takes place.

Just keep watch that the male does not harass her so much that she is unable to feed, or is otherwise stressed (the bites usually do no damage). In nature, it rains often during the warmest part of the year in the crocodile skink’s habitat, and is drier when temperatures cool a bit. Arranging this type of cycle at home, if possible, may bring them both into breeding condition.

The fact that your pair is out by day is fortunate – we know very little about these lizards, so any observations you might record should prove very interesting…please pass along your thoughts and keep me posted.

They are one of my all time favorites. I especially like the T.novaguniea they have a very attractive orange hue on there backs, around the eyes are solid white in some individuals very cool species. I understand Dallas zoo has very good luck with captive reproduction.

I have a pair of red eyed crocodile skinks. The stool came back positive for Pharyngodon pinworms. They are eating well and one will actually feed in front of me (although both hide 90% of the time, as expected, the second will grab an earthworm out of my hand from his hide box when I dangle it at the entrance hole). My question is the likelihood of those parasites harming them and if I should treat as you note sometimes they reacted badly to meds.

Pinworms show up commonly in so many species, both imports and CB animals; tortoises kept outdoors, etc…but effects may vary with species of pinworm and host; also populations may be able to build up in captivity. At the zoo we always treated, but I do not recall anything specifically re crocodile lizards…I’d go with your vet’s advice…let me know if you need a second opinion, I have a list of experienced vets in USA and for some other countries. best, frank

About Frank Indiviglio

Being born with a deep interest in animals might seem unfortunate for a native Bronxite , but my family encouraged my interest and the menagerie that sprung from it. Jobs with pet stores and importers had me caring for a fantastic assortment of reptiles and amphibians. After a detour as a lawyer, I was hired as a Bronx Zoo animal keeper and was soon caring for gharials, goliath frogs, king cobras and everything in-between. Research has taken me in pursuit of anacondas, Orinoco crocodiles and other animals in locales ranging from Venezuela’s llanos to Tortuguero’s beaches. Now, after 20+ years with the Bronx Zoo, I am a consultant for several zoos and museums. I have spent time in Japan, and often exchange ideas with zoologists there. I have written books on salamanders, geckos and other “herps”, discussed reptile-keeping on television and presented papers at conferences. A Master’s Degree in biology has led to teaching opportunities. My work puts me in contact with thousands of hobbyists keeping an array of pets. Without fail, I have learned much from them and hope, dear readers, that you will be generous in sharing your thoughts on this blog and web site. For a complete biography of my experience click here.

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